1. Field of the Invention
The invention relates to the formation of road-type coatings and pertains more specifically to a process of obtaining a bonding layer enabling the gluing of a layer made of bituminous coated materials onto a support.
The invention also relates to a road-type coating comprising a bonding layer obtained by the process.
The invention relates furthermore to a road making machine allowing the implementation of this process.
2. Discussion of Background
The production of a road-type coating results from the formation of successive layers. Among the various layers, at least one bituminous layer covers an inferior layer, so-called supporting layer. The nature of the supporting layer can be quite varied, concrete, cobble stones or bituminous coatings for instance. The condition of this support can also be subject to many variations. The support may be new or old, poor or sweating, rough or smooth, damp or dry, dusty or not, etc.
A bonding layer ensures proper gluing between the bituminous layer and its support. The bonding layer also guarantees the impermeability of the roadway. Generally, one avoids making the layer from an anhydrous bonding material which exhibits a risk of trapping fluxes between both layers situated on either side and which requires small amounts of bituminous bonding material which are incompatible with conventional spreading means: 300 to 600 grams of residual bitumen per square meter.
According to certain embodiments, the roadway comprises several successive layers of coated materials. These layers are linked together by a bonding layer. The inferior layer of coated materials thus serves as a supporting layer, for the bonding layer.
In some cases, the superior layer of the roadway may exhibit a superficial coating. This coating may provide certain surface qualities, such as roughness and impermeability, which the coating might have lost due to wear and tear. The coating layers are made of carbohydrated bonding materials, fluidized for spreading, either in an aqueous emulsion form or by adding to the bituminous small fractions of oil or coal distillation. The coatings may be anhydrous coatings, mixtures of bitumens and carbohydrated products.
Many studies have stressed the importance and the necessary proprieties of the bonding layer. Bonding layers of insufficient quality generate separation phenomena of the layers composing the roadway. This frequently encountered phenomenon requires heavy and expensive maintenance. Industry standards specify that the bonding layer must be regular and continuous and should never be sanded.
This bonding layer is generally composed of an alkaline emulsion of pure bitumen or of modified bitumen. The usual dosages recommended range between 300 and 600 g of residual bitumen per square meter. The dosage depends on the condition of the support and on the nature of the coated materials employed.
At present, there are several methods for forming a bonding layer.
According to one conventional method, an emulsion layer is deposited by a spreading machine, comprising a tank and a spreading ramp. The application is performed over a few dozen, sometimes a few hundred meters, ahead of an implementation workshop and the depositing of a bituminous coated material.
This method, although quite current, is only marginally satisfactory and exhibits many shortcomings. The breaking duration of the emulsions used generally exceeds 30 minutes, so that the tires of the trucks supplying the yard with materials, travelling on the fresh layer, reduce the thickness of the layer in some places and cause pollution by spreading bitumen to the roads the trucks take later. On the other hand, portions of the bonding layer are carried away by the caterpillars of the finisher travelling on the bonding layer, which finisher serves to deposit the layer made of coated materials. This premature degradation of the bonding layer causes the emulsion to resurface through the coated material in some places leading to glazing of the coated surface.
When the support exhibits poor cohesion, plate-like separation of the bonding layer, catching some of the supporting elements, leads to the formation of holes and bumps. In all cases, the defect in the bonding layer between both layers made of bituminous materials also causes very irregular and in sufficient gluing of those layers with respect to one another.
It has been suggested, for some years, to use devices associated with the finisher, which enable application of the bonding layer just before the coated material. However, this method also shows many shortcomings.
When the spreading means are arranged at the front of the finisher, the wheels or the caterpillars of the mobile assembly will circulate on the freshly spread layer, thereby causing deterioration of the layer. Besides, since the finishers are designed for producing coatings of roadways of variable breadth, a device fitted with adjustable ramps should therefore be provided. Moreover, the displacement velocity of finishers (3 m/min to 6 m/min) is much slower than the velocity of classic spreaders (30 m/min to 150 m/min). Consequently, the flow rate of the bonding material must be suited accordingly. The combination of those conditions yields a complex ramp arrangement, and delicate adjustment conditions, which are unlikely to yield homogeneous bonding layers.
This method also causes procurement difficulties of the various materials, on the vehicles, whose re-supplying is not always synchronized.
According to this method, the emulsion is dried and broken in a very short time, by contact of the bonding layer with the hot coated materials. Consequently, the bonding layer thus obtained cannot be controlled from either a quantitative or a qualitative viewpoint.
It has also been suggested to form a bonding layer by depositing thin capsules containing an anhydrous bituminous bonding agent. These capsules contain a husk made of solid material, stable at room temperature, which melt and vanish at the temperature of the applied coated material in order to release the bonding agent. This idea is quite tricky to implement and does not enable homogeneous distribution of the bonding layer over the whole surface of the support.
In particular, poor gluing causes systematic weakness in the structure of the roadway and faster fatigue deterioration.